Systems for detecting fault gases, moisture and breakdown products dissolved in a fluid contained in an electrical system such as a transformer, a circuit breaker or any electric apparatus using a dielectric fluid as an insulating substance are well known in the art and have been described in prior art.
Such systems are described in Canadian Patent no. 1,054,223 (Belanger), U.S. Pat. No. 4,293,399 (Belanger et al) and U.S. Pat. No. 4,271,474 (Belanger et al). For example, the concentration of gaseous hydrogen dissolved in a fluid is determined by a measure of an electric current generated by electro-chemical oxidation of the gaseous hydrogen at an electrode of detection. The prior art detecting and measuring device comprises a polymeric membrane permeable to hydrogen gas in contact with the fluid; an electrolyte capable of producing oxidation of the hydrogen gas diffused through the polymeric membrane at a first electrode and reduction of an oxygen-containing gas such as air at a second electrode; a measuring device connected across the electrode for measuring the intensity of the electrical current generated by the electro-chemical reaction of oxidation of the hydrogen gas, this intensity being proportional to the concentration of hydrogen in the fluid.
Such detection devices are essential to provide an accurate diagnosis of the incorrect operation of transformers, circuit breakers, reactance or any electro-apparatuses using a dielectric fluid such as oil or SF6 gas as insulating substance. It is indeed well-known that, in the event of a disturbance or malfunction of one of the above mentioned apparatuses due to a too high working temperature or a high electrical discharge, there is production of gases in the insulating fluid. Failure conditions may also produce moisture or breakdown products in the insulating fluid. Accordingly, it can be easily understood that the utilization of a device allowing for immediate detection of an increase of the concentration of gases, moisture or breakdown products dissolved in the insulating fluid, is advantageous since it allows immediate diagnosis of the incorrect operation of the electrical apparatus on which the device is mounted, and when this incorrect operation is timely located, to avoid irreparable ruin of the apparatus.
These prior art devices have the drawback that the sample received by the detector may not be uniform or representative of the fluid contained in the electrical system at a given moment in time. For example, in U.S. Pat. No. 4,293,399, the detector is attached to the wall of the electrical apparatus and the fluid must passively diffuse to that area to reach the detector. Such a passive sampling system has two inherent problems. Firstly, the sample that does reach the detector may not be uniform, and secondly if gases, moisture or breakdown products are introduced at some point in the system, which is remote from the detector, it may take considerable time before they will be detected.
Therefore it is desirable to develop a system whereby the sample of the fluid tested is an accurate representation of the actual fluid and the time required to detect gases, moisture or breakdown products is kept to a minimum.
Because such devices are sensitive to temperature fluctuations, it is desirable to provide a means whereby the temperature of the system can be regulated.
It is also desirable that the sampling and detecting apparatus be easily installed onto existing electrical systems.